Where did you here this cali??? sounds like bad advise! to me
never heard of this(water with ph 4.0?) gotta link to your so called theory...solution to his def? and not good for drastic flux in ph???
http://retirees.uwaterloo.ca/~jerry/orchids/light.html
The Orchid House
pH: WHAT DOES IT MEAN?
The term pH refers to the alkalinity or acidity of a growing media water solution. This solution consists of mineral elements dissolved in ionic form in water. The reaction of this solution whether it is acid, neutral or alkaline will have a marked effect on the availability of mineral elements to plant roots. When there is a greater amount of hydrogen H+ ions the solution will be acid (<7.0). If there is more hydroxyl OH- ions the solution will be alkaline (>7.0). A balance of hydrogen to hydroxyl ions yields a pH neutral soil (=7.0).
The range for most crops is 5.5 to 6.2 or slightly acidic. This creates the greatest average level for availability for all essential plant nutrients. Extreme fluctuations of higher or lower pH can cause deficiency or toxicity of nutrients.
(copied from Orchid House...in link)
...but hey what does anyone else know...those are not my words....